Microscale chemical effects of low temperature alteration of DSDP basaltic glasses

Abstract

A novel application of X ray fluorescence, using selected area analysis, has been used to study the effect of low temperature alteration on trace elements in DSDP basaltic glasses. Major and minor element distributions were detailed through the use of electron microprobe analyses on the same sample areas. Samples include pillow basalt rinds and hyaloclastite sections from Deep Sea Drilling Project Site 396B. The glasses were found to release approximately 50% of the original Si and Al, 65% of the Mg and Na, and over 90% of the Ca originally present, during alteration to palagonite. Fe and Ti were found to be immobile, and K was increased 40‐fold by concentration from seawater. For the trace metals, over 25% of the Zn, Cu, and Ni were released, 40% of the Mn, and over 10% of the Cr. These changes apply only to the conversion of fresh glass (sideromelane) to palagonite (smectite) and do not include the effects of authigenic phillipsite and calcite reprecipitated locally. Differences between the effects of low temperature weathering on the crystalline basalts and the glasses appear to be primarily a function of the susceptibility of the primary mineral phases to attack, with the glass, as the least stable phase, most altered.